I have just flashed mine to the 900Mhz kernel from Lehto. (125-900)

Here's some of my quick comparison. Before flash and after.

------600mhz--------

250mhz 12% during idle
500mhz 9% during charging

35sec HAM launch till downloads show up
20sec daum.net via MicroB
08sec sygic map loaded
09sec time to show tweego login screen

-------900mhz--------

125mhz 14% during idle
500mhz 8% during charging

26sec HAM launch till downloads show up
12sec daum.net via MicroB
06sec sygic map loaded
05sec time to show tweego login screen